JP2022083615A - Combustion chamber structure for engine - Google Patents

Abstract

To provide a combustion chamber structure for an engine capable of improving engine output while suppressing knocking.SOLUTION: A combustion chamber 6 for an engine is defined by a crown surface 50 of a piston 5, the inner wall surface of a cylinder 2 and a pent-roof type ceiling surface 6U. The crown surface 50 includes an exhaust side bottom part 51 arranged near the edge on the exhaust side, an intake side bottom part 52 arranged near the edge on the intake side, an exhaust side inclined surface 53 rising from the exhaust side bottom part 51 to the center part of the crown surface 50, an intake side inclined surface 54 rising from the intake side bottom part 52 to the center part of the crown surface 50, and a plane 55 and an inter-recess plane 56, the plane 55 being provided continuously between the upper end of the exhaust side inclined surface 53 and the upper end of the intake side inclined surface 54, and extending from the center part of the crown surface 50 in the direction perpendicular to a cylinder axis AX, the inter-recess plane 56 being arranged between a pair of recess parts 531 of the exhaust side inclined surface 53 and continuous with the plane 55 in the same plane.SELECTED DRAWING: Figure 8

Description

The present invention relates to a combustion chamber structure of an engine having a combustion chamber having a pent-roof type ceiling surface.

Daily research is being conducted on the structure of the combustion chamber of an engine, especially the structure of a piston, for the purpose of improving thermal efficiency and fuel efficiency. For example, Patent Document 1 discloses a structure in which a combustion chamber provided with a pent-roof type ceiling surface is provided with a cavity on the crown surface of the piston and an inclined surface along the shape of the ceiling surface. According to this combustion chamber structure, deceleration of the tumble flow is suppressed, combustion is promoted, and fuel efficiency is improved.

A simple and effective means for improving fuel efficiency is to set a high compression ratio. However, when the compression ratio is set to high, for example, in the operating region of low rotation and high load, the combustion chamber pressure and temperature at the compression end rise excessively, inducing abnormal combustion. This abnormal combustion is based on the steep self-ignition of unburned fuel gas before the completion of flame propagation combustion, which causes knocking.

Japanese Unexamined Patent Publication No. 2018-162733

Conventionally, in order to prevent the above-mentioned knocking from occurring, measures have been taken to intentionally suppress the engine output. Specifically, the fuel injection timing to the combustion chamber and the ignition timing to the air-fuel mixture are devised to retard the combustion center of gravity and suppress the engine output. Since such means prevent the engine from increasing in output, we would like to avoid it as much as possible. The structural ingenuity of the combustion chamber disclosed in Patent Document 1 can also contribute to the improvement of fuel efficiency, but according to further research by the present inventors, it is not sufficient from the viewpoint of maintaining the tumble flow until the latter half of the compression stroke. It has been found.

An object of the present invention is to provide a combustion chamber structure of an engine capable of improving engine output while suppressing knocking.

The combustion chamber structure of the engine according to one aspect of the present invention is partitioned by a crown surface of a piston, an inner wall surface of a cylinder in which the piston is slidably accommodated, and a pent roof type ceiling surface formed on a cylinder head. It is a combustion chamber structure of an engine provided with a combustion chamber, and on the ceiling surface, an opening of two intake ports for supplying intake air to the combustion chamber and two exhaust ports for discharging exhaust from the combustion chamber. When the side on which the intake port is arranged is the intake side and the side on which the exhaust port is arranged is the exhaust side, the crown surface is the end of the crown surface on the exhaust side. An exhaust side bottom portion arranged near the edge, an intake side bottom portion arranged near the intake side end edge, and an inclined surface rising from the exhaust side bottom portion toward the central portion of the crown surface. An exhaust-side inclined surface having a pair of recesses for avoiding interference with exhaust valves arranged in each of the two exhaust ports, and an intake-side inclined surface that rises from the intake-side bottom to the center of the crown surface. A first plane that is continuously provided between the upper end of the exhaust side inclined surface and the upper end of the intake side inclined surface and extends in a direction orthogonal to the axial direction of the cylinder at the central portion of the crown surface. It is characterized by having a second plane which is arranged between the pair of recess portions of the exhaust side inclined surface and which is continuous in the same plane as the first plane.

According to this combustion chamber structure, since the intake port is formed on the ceiling surface of the pent-roof type, it becomes a combustion chamber in which a tumble flow is formed. The crown surface of the piston is raised in a convex shape by the inclined surface on the exhaust side and the inclined surface on the intake side, and a continuous flat surface is formed in the central portion thereof. The "continuous plane" means a plane in which there are no dents such as cavities.

By forming a continuous first plane, the tumble flow can flow along the first plane without being obstructed by a depression such as a cavity. Further, since the second plane is arranged between the pair of recess portions on the exhaust side inclined surface, the tumble flow can be guided by the second plane. Therefore, it is possible to prevent the tumble flow from colliding with the boundary portion between the exhaust side inclined surface and the first plane between the pair of recess portions and being weakened. By these structural measures, the resistance of the piston crown surface to the tumble flow can be reduced, and the tumble flow can be maintained until the latter half of the compression stroke. When the tumble flow collapses, turbulent energy is generated. Maintaining the tumble flow leads to maintaining the turbulent energy possessed by the tumble flow in a high state. Therefore, it is possible to increase the combustion speed by collapsing the tumble flow in the latter half of the compression stroke and generating high turbulent energy. As a result, combustion can be completed before the occurrence of self-ignition, which causes knocking. Further, since knocking can be suppressed, it is possible to avoid control that intentionally suppresses engine output such as retarding the center of gravity of combustion. As a result, a high compression ratio can be achieved.

In the combustion chamber structure, when the direction from the intake side to the exhaust side is the first direction, the second plane extends in the first direction from the side side of the first plane on the exhaust side. The extension length of the second plane is set to be at least 1/4 or more of the width of the recess portion in the first direction in the top view of the crown surface. desirable.

According to this combustion chamber structure, the second plane is a plane extending to the exhaust side with an appropriate length between the pair of recess portions. Therefore, the second plane makes it easier to guide the tumble flow from the exhaust side to the intake side.

In the above combustion chamber structure, it is desirable that an ignition portion for realizing flame propagation combustion in the combustion chamber is arranged on the ceiling surface facing the first plane.

The intake air compressed without weakening the tumble flow is in a state where the turbulent energy is high at the position facing the first plane. By arranging the ignition unit at such a position, the combustion speed of flame propagation combustion can be increased.

In the above combustion chamber structure, it is desirable that a fuel injection unit that injects fuel into the combustion chamber is arranged on the intake side of the combustion chamber.

According to this combustion chamber structure, the fuel sprayed from the fuel injection portion can be easily put on the tumble flow, and a homogeneous air-fuel mixture can be formed in the combustion chamber.

In the above combustion chamber structure, the intake side inclined surface is provided with a pair of intake recess portions for avoiding interference with intake valves arranged in the two intake ports, respectively, and the pair of intake air on the intake side inclined surface. It is desirable to further include a third plane that is arranged between the recess portions and is continuous in the same plane as the first plane.

According to this combustion chamber structure, the tumble flow can be guided above the combustion chamber along the third plane. That is, it is possible to prevent the tumble flow from flowing along the intake side inclined surface and colliding with the intake side inner wall surface of the cylinder to be weakened.

In the above combustion chamber structure, it is desirable that the geometric compression ratio of the cylinder is set within the range of 13.5 or more and 15.5 or less. This makes it possible to improve fuel efficiency.

According to the present invention, it is possible to provide an engine combustion chamber structure capable of improving engine output while suppressing knocking.

FIG. 1 is a schematic cross-sectional view of an engine to which the combustion chamber structure of the engine according to the present invention is applied. FIG. 2 is a schematic perspective view showing the structure of one cylinder included in the engine body. FIG. 3 is a schematic plan view showing the structure of the intake / exhaust system of the cylinder and its vicinity. FIG. 4 is a perspective view of the piston. FIG. 5 is a plan view of the crown surface of the piston. FIG. 6 is a side view of the crown surface of the piston. FIG. 7 is a sectional view taken along line VII-VII of FIG. FIG. 8 is a perspective view of the piston with various parameters related to the crown surface of the piston. FIG. 9A schematically shows the flow of the tumble flow in the combustion chamber according to the embodiment of the present invention, and FIG. 9B schematically shows the flow of the tumble flow in the combustion chamber according to the comparative example. It is a figure. 10 (A) and 10 (B) are diagrams schematically showing the flow of the tumble flow in the combustion chamber according to the comparative example. FIG. 11 is a tabular diagram showing the structure and parameters of the piston crown surface according to Examples 1 and 2 of the present invention. FIG. 12 is a tabular diagram showing the structure and parameters of the piston crown surface according to Examples 3 and 4 of the present invention. FIG. 13 is a tabular diagram showing the structure and parameters of the piston crown surface according to the fifth and comparative examples of the present invention. 14 (A) and 14 (B) are perspective views of a piston for explaining the action of the second plane. FIG. 15 is a plan view of the crown surface of the piston according to the modified example of the present invention.

[Overall engine configuration]
Hereinafter, the combustion chamber structure of the engine according to the embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an engine to which the combustion chamber structure according to the embodiment of the present invention is applied. The engine shown here is a multi-cylinder gasoline engine mounted on the vehicle as a power source for driving a vehicle such as an automobile. The engine includes an engine main body 1 and an auxiliary machine such as an intake / exhaust manifold and various pumps (not shown) attached to the engine main body 1.

The engine body 1 includes a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the cylinder 2 from above, and a piston 5 housed in the cylinder 2. And have. The engine body 1 is typically a multi-cylinder type having a plurality of (for example, four) cylinders, but only one cylinder 2 is shown in FIG. 1 for simplification.

FIG. 2 shows a schematic perspective view of one cylinder 2. The piston 5 is a substantially cylindrical body having an outer diameter corresponding to the bore diameter Lb of the cylinder 2, and is housed in the cylinder 2 so as to be reciprocally slidable with a predetermined stroke Ls. As will be described in detail later, the crown surface 50, which is the upper surface of the piston 5, is raised in a convex shape and is provided with a plane 55 having a mountain height h. Below the piston 5, a crank shaft 7, which is an output shaft of the engine body 1, is provided. The crank shaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis according to the reciprocating motion of the piston 5.

A combustion chamber 6 is defined above the piston 5. The fuel is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. The supplied fuel burns while being mixed with air in the combustion chamber 6, and the piston 5 pushed down by the expansion force due to the combustion reciprocates in the vertical direction. The combustion chamber 6 includes an inner wall surface of the cylinder 2, a crown surface 50 of the piston 5, and a combustion chamber ceiling surface 6U (including each valve surface of the intake valve 11 and the exhaust valve 12) formed on the bottom surface of the cylinder head 4. It is partitioned by. The combustion chamber ceiling surface 6U is a ceiling surface having a pent-roof shape that is convex upward.

The geometric compression ratio of the cylinder 2, that is, the ratio of the volume of the combustion chamber 6 when the piston 5 is at the top dead center and the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center is 13.5 or more. It is desirable to set it to a high compression ratio. The range of the preferable compression ratio is 13.5 or more and 15.5 or less. By setting such a high compression ratio, fuel efficiency can be improved.

The pent-roof type combustion chamber ceiling surface 6U is formed with an intake port 9 and an exhaust port 10 that open toward the combustion chamber 6. The intake port 9 is a port for supplying intake air to the combustion chamber 6. The intake port 9 of the present embodiment is a tumble port capable of forming a tumble flow (vertical vortex). In FIG. 2, the flow direction of the tumble flow Ft is added. The exhaust port 10 is a port for exhausting the exhaust gas after combustion from the combustion chamber 6. The combustion chamber ceiling surface 6U is provided with an intake valve 11 for opening and closing the intake port 9 and an exhaust valve 12 for opening and closing the exhaust port 10.

As shown in FIGS. 2 and 3, the valve type of the engine of the present embodiment is a four-valve type of two intake valves and two exhaust valves having two intake ports and two exhaust ports. FIG. 3 is a schematic plan view showing the structure of the intake / exhaust system of the cylinder 2 and its vicinity. The intake port 9 has a first intake port 9A and a second intake port 9B. The exhaust port 10 has a first exhaust port 10A and a second exhaust port 10B. One intake valve 11 is provided for each of the first intake port 9A and one for the second intake port 9B, and one exhaust valve 12 is provided for each of the first exhaust port 10A and the second exhaust port 10B. Has been done.

As shown in FIG. 3, of the first and second intake ports 9A and 9B, the second intake port 9B is provided with a swirl valve 17 capable of opening and closing the second intake port 9B. When the swirl valve 17 is driven in the closed direction, the proportion of intake air flowing into the combustion chamber 6 from the first intake port 9A in which the swirl valve 17 is not provided increases. Therefore, it is possible to strengthen the swirling flow, that is, the swirl flow, which swirls around the cylinder shaft AX (the central shaft of the combustion chamber 6). In FIG. 3, the flow direction of the swirl flow Fs is added. On the contrary, if the swirl valve 17 is driven in the open direction, the swirl flow Fs can be weakened. As described above, since the intake port 9 is a tumble port, the swirl flow Fs formed when the swirl valve 17 is closed becomes a diagonal swirl flow mixed with the tumble flow Ft.

The cylinder head 4 is provided with an intake side valve mechanism 13 for driving the intake valve 11 and an exhaust side valve mechanism 14 for driving the exhaust valve 12. These valve valves 13 and 14 drive the intake valve 11 and the exhaust valve 12 so as to be interlocked with the rotation of the crank shaft 7. By this drive, the valve head of the intake valve 11 opens and closes the opening of the intake port 9, and the valve head of the exhaust valve 12 opens and closes the opening of the exhaust port 10. The valve operating mechanisms 13 and 14 incorporate a variable valve timing mechanism (not shown) that changes the opening / closing timing.

An injector 15 (fuel injection section) and a spark plug 16 (ignition section) are assembled to the cylinder head 4. The injector 15 injects fuel supplied from the fuel system (not shown) into the combustion chamber 6. The injector 15 is a peripheral edge of the combustion chamber ceiling surface 6U, and is arranged on the intake side where the intake port 9 is arranged. With such an arrangement, the fuel sprayed from the injector 15 joins the tumble flow Ft, and the fuel is easily distributed throughout the combustion chamber 6 on the tumble flow Ft. That is, a homogeneous air-fuel mixture can be formed in the combustion chamber 6.

The spark plug 16 ignites a mixture of fuel injected from the injector 15 into the combustion chamber 6 and air introduced into the combustion chamber 6 through the intake ports 9 (9A, 9B). The spark plug 16 is attached to the cylinder head 4 so as to be along the cylinder shaft AX. The ignition electrode portion of the spark plug 16 is exposed in the combustion chamber 6 at the radial center of the combustion chamber ceiling surface 6U and faces the flat surface 55 of the crown surface 50 of the piston 5. When ignition energy is supplied from the spark plug 16 to the air-fuel mixture in the combustion chamber 6, flame propagation combustion occurs in the combustion chamber 6 starting from the ignition point.

[Detailed structure of piston]
Subsequently, with reference to FIGS. 4 to 7, the structure of the piston 5, particularly the structure of the crown surface 50, will be described in detail. In the present embodiment, the crown surface 50 is provided with a shape device that enables the above-mentioned tumble flow Ft to be maintained near the compression top dead center. 4 is a perspective view of the piston 5 shown in FIGS. 1 and 2, FIG. 5 is a plan view of the crown surface 50 of the piston 5, FIG. 6 is a side view of the crown surface 50, and FIG. 7 is FIG. It is a sectional view taken along the line VII-VII of.

In FIGS. 4 to 7, in order to ensure the clarity of the explanation, the direction of XYZ is indicated. The Z direction corresponds to the cylinder axis AX direction, the X direction corresponds to the front-rear direction of the engine body 1 which is the extension direction of the crank shaft 7, and the Y direction corresponds to a direction orthogonal to both the Z direction and the X direction. In each figure, the front side, the rear side in the installation direction of the engine body 1, the F side (+ X), the R side (-X), and the intake side (IN side) in the sense that the intake port 9 is arranged. ; + Y), the exhaust side (EX side; -Y) in the sense that the exhaust port 10 is arranged, and the upper (+ Z) and lower (-Z) in the sense of the upper side and the lower side on the cylinder shaft AX. Is attached.

The piston 5 includes a piston head 5A and a skirt portion 5B connected to the lower side (-Z side) of the piston head 5A. The piston head 5A is made of a cylindrical body, and includes a crown surface 50 forming a part (bottom surface) of the wall surface of the combustion chamber 6 on the upper surface, and a side peripheral surface 5C that is in sliding contact with the inner wall surface of the cylinder 2. The side peripheral surface 5C is provided with a plurality of ring grooves into which the piston ring is fitted. The skirt portion 5B is arranged on the + Y side and the −Y side of the piston head 5A, and suppresses swinging swing during the reciprocating motion of the piston 5. At the center of the skirt portion 5B in the Y direction, a piston boss 5D for partitioning a pin hole extending in the X direction is provided. A piston pin for connecting to the connecting rod 8 is inserted through the piston boss 5D.

The crown surface 50 is a substantially circular surface facing the combustion chamber ceiling surface 6U in the Z direction. The crown surface 50 includes an exhaust side bottom portion 51, an intake side bottom portion 52, an exhaust side inclined surface 53, an intake side inclined surface 54, a plane 55 (first plane), a recess-to-recess plane 56 (second plane), an F side side wall 57, and the crown surface 50. The R side side wall 58 is included. Of these parts, the exhaust side bottom 51 and the intake side bottom 52 are the base surfaces having the lowest height in the + Z direction on the crown surface 50, and the other parts are raised by the mountain height h in the + Z direction from the base surface. It constitutes a raised part.

The exhaust side bottom 51 and the intake side bottom 52 are planes extending in the XY direction orthogonal to the cylinder axis AX, and are at the same height position in the Z direction. The exhaust side bottom portion 51 and the intake side bottom portion 52 may be a surface having a slight inclination with respect to the XY direction, or a surface having a slightly convex or concave curved surface. The exhaust side bottom portion 51 is arranged near the end edge of the crown surface 50 on the EX side (−Y). The intake side bottom portion 52 is arranged near the edge of the crown surface 50 on the IN side (+ Y).

The exhaust side bottom portion 51 is a bow-shaped plane having an arc on the outer peripheral edge on the −Y side (side peripheral surface 5C) of the crown surface 50 and a straight line extending in the X direction as a chord. The bottom portion 52 on the intake side is an arcuate plane having an arc on the outer peripheral edge on the + Y side of the crown surface 50 and a straight line extending in the X direction as a chord. The exhaust side bottom 51 and the intake side bottom 52 are squish areas where a squish flow is formed when the piston 5 heads toward the compression top dead center. In the present embodiment, the surface area of the intake side bottom 52 is set to be wider than the surface area of the exhaust side bottom 51.

The exhaust side inclined surface 53 is an inclined surface that gradually rises from the exhaust side bottom portion 51 toward the center portion in the Y direction of the crown surface 50 (the radial center portion of the crown surface 50). The lower end of the exhaust side inclined surface 53 is connected to the + Y end edge of the exhaust side bottom portion 51, and the upper end is connected to the −Y end edge of the plane 55 and the recess plane 56. The exhaust side inclined surface 53 includes a pair of recess portions 531 on the + X side and the −X side, and a recess intersection portion 532 located in these recess portions 531. The recess portion 531 is a substantially semicircular recess for avoiding interference with the exhaust valves 12 arranged in the first and second exhaust ports 10A and 10B. The recess intersection portion 532 has a lower bottom edge connected to the exhaust side bottom portion 51 and an upper end edge connected to the recess intersection plane 56 located in the pair of recesses 531 as an upper bottom in a plan view in the + Z direction (FIG. 5). It has a substantially trapezoidal shape. The inclination angles of the recess portion 531 and the recess intersection portion 532 with respect to the Y direction are set to be the same. The inclination angles may be slightly different.

The intake side inclined surface 54 is an inclined surface that gradually rises from the intake side bottom portion 52 toward the central portion of the crown surface 50 in the Y direction. The lower end of the intake side inclined surface 54 is connected to the −Y end edge of the intake side bottom portion 52, and the upper end is connected to the + Y end edge of the plane 55. In the present embodiment, in a plan view in the + Z direction, both the lower end and the upper end of the intake side inclined surface 54 are edges extending linearly in the X direction. The intake side inclined surface 54 is exemplified as a simple inclined plane, but when interference with the intake valve 11 occurs, a recess portion similar to the exhaust side recess portion 531 is provided (exemplified in FIG. 15 described later). is doing).

The plane 55 (first plane) is a plane extending in the XY direction orthogonal to the cylinder axis AX at the central portion of the crown surface 50 in the Y direction. The plane 55 is a plane continuously provided between the upper end of the exhaust side inclined surface 53 and the upper end of the intake side inclined surface 54. The "continuous plane" means a plane in which there are no dents such as cavities. Further, the plane 55 may be a surface having a slight inclination with respect to the XY direction or a surface having a slightly convex or concave curved surface as long as the flow of the tumble flow Ft is not substantially hindered.

More specifically, the plane 55 has a substantially rectangular shape that is long in the X direction in a plan view in the + Z direction. The plane 55 has a first EX edge 551 and a second EX edge 552 as side sides on the −Y side, and an IN end edge 553 as a side side on the + Y side. The first EX end edge 551 is connected to the upper end of the recess portion 531 on the + X side. The second EX end edge 552 is connected to the upper end of the recess portion 531 on the −X side. The IN end edge 553 is connected to the upper end of the intake side inclined surface 54. The + X side and the −X side side sides of the plane 55 have an arcuate shape along the circumference of the side peripheral surface 5C.

The recess-to-recess plane 56 (second plane) is a plane arranged between the pair of recess portions 531 of the exhaust side inclined surface 53. The inter-recess plane 56 is also a plane extending in the XY direction, and is a plane existing in the same plane as the plane 55, that is, a plane located at the same height in the Z direction as the plane 55. The recess-to-recess plane 56 is a plane continuous with the plane 55. The plane 55 and the recess plane 56 form the top surface of the raised portion of the crown surface 50, and are the surfaces having the highest height in the + Z direction.

The recess-to-recess plane 56 extends from the center of the side of the plane 55 on the −Y side in the X direction toward the −Y side, in other words, from between the first EX edge 551 and the second EX edge 552. It is formed so as to extend to the side. The EX end edge 561 of the recess space plane 56 is connected to the upper end of the recess space portion 532 of the intake side inclined surface 54. The recess-to-recess plane 56 is located so as to be sandwiched between the upper ends of the pair of recess portions 531 and has a substantially square shape in a plan view in the + Z direction.

With reference to FIG. 5, the extension length of the recess plane 56 will be described. The recess-to-recess plane 56 is formed so as to extend from the side side of the plane 55 on the −Y side (exhaust side) in the −Y direction (first direction from the intake side to the exhaust side). In FIG. 5, the extension length of the recess-to-recess plane 56 is shown by d1. Further, the width of the pair of recess portions 531 in the Y direction is indicated by d2. d2 is the distance between the EX edge edges 551 and 552 and the most −Y side peripheral edge of the recess portion 531 in the top view of the crown surface 50. Regarding the relationship between d1 and d2, it is desirable that d1 is set to a length of 1/4 or more of d2 as long as the recess plane 56 does not interfere with the combustion chamber ceiling surface 6U. In this case, the recess-to-recess plane 56 is a plane extending from the plane 55 to the exhaust side with an appropriate length between the pair of recess portions 531. Therefore, the recess-to-recess plane 56 makes it easier to guide the tumble flow from the exhaust side to the intake side.

[Characteristics of piston crown surface]
FIG. 8 is a diagram showing various parameters related to the crown surface 50 of the piston 5. In the figure, the mountain height h, the width Lie and the front-rear width Lfr of the plane 55, the exhaust side inclined surface angle Exd, the surface area S1 of the plane 55 and the plane between recesses 56, the surface area S2 of the exhaust side inclined surface 53, and the intake side inclined surface. The surface area S3 of 54 is shown.

The mountain height h is the height in the Z direction from the exhaust side bottom portion 51 or the intake side bottom portion 52, which is the base surface of the crown surface 50, to the plane 55 and the recess space plane 56, which are the top surfaces. The lateral width Lie is the width in the Y direction of the plane 55 (the direction in which the intake side and the exhaust side face each other). The front-back width Lfr is the width in the X direction of the plane 55. The side sides of the plane 55 on the + X side and the −X side are arc sides. The front-back width Lfr is the width in the X direction between the portions where these arc sides extend most to the + X side or the −X side. The exhaust side inclined surface angle Exd is an inclined angle of the exhaust side inclined surface 53 with respect to the Y direction. In the present embodiment, since the plane 55 is a horizontal plane along the Y direction, the inclined surface angle Exd is an angle formed by the plane 55 and the exhaust side inclined surface 53.

The surface area S1 is the total surface area of the surface area of the plane 55 and the surface area of the recess-to-recess plane 56. The surface area of the plane 55 is the area of the portion surrounded by the side sides of the + X side and the −X side and the side sides of the + Y side and the −Y side that partition the plane 55. It is the area calculated by multiplying by. The recess-to-recess plane 56 is the surface area of the portion extending in the −Y direction from the plane 55. By attaching the recess-to-recess plane 56 to the plane 55, the surface area S1 can be made larger.

The surface area S2 of the exhaust side inclined surface 53 is the total area of the surface area of the pair of recess portions 531 and the surface area of the recess inter-recess portion 532. The stepped portion 53A existing between the recess portion 531 and the recessed portion 532 is not included in the surface area S2. This is because the step portion 53A does not substantially affect the flow of the tumble flow Ft. Further, the recess inter-recess section 532 may include a recess lower portion 533 (specified in Example 3 and others described later) extending not only between the recess sections 531 but also below the recess section 531. The surface area S2 in this case also includes the surface area of the recess lower part 533.

In the example of FIG. 8, the surface area S3 of the intake side inclined surface 54 is simply the area of the inclined plane constituting the intake side inclined surface 54. When a recess portion for avoiding interference with the intake valve 11 is also formed on the intake side inclined surface 54 (example of FIG. 15), the total area of the surface area of the recess portion and the surface area of the recess inter-recess portion. Will be.

In the present embodiment, in order to reduce the resistance of the crown surface 50 of the piston 5 to the tumble flow Ft and maintain the tumble flow Ft until the latter half of the compression stroke, the above surface areas S1, S2, and S3 have the following features (1) to. (3) is set to be provided.
(1) The surface area S1 obtained by adding the plane 55 and the recess plane 56 is larger than the surface area S2 of the exhaust side inclined surface 53.
(2) Preferably, the surface area S1 is larger than the surface area S3 of the intake side inclined surface 54.
(3) More preferably, the surface area S1 is larger than the sum of the surface area S2 of the exhaust side inclined surface 53 and the surface area S3 of the intake side inclined surface 54.

[Significance of the characteristic part of the crown surface]
The significance of the above features (1) to (3) will be described with reference to FIGS. 9 and 10. FIG. 9A is a schematic view showing the flow of the tumble flow Ft when the crown surface 50 of the piston 5 satisfying the features (1) to (3) and the bottom surface of the combustion chamber 6 is formed. The intake air introduced into the combustion chamber 6 from the intake port 9 (tumble port) arranged on the ceiling surface 6U of the pent-roof type combustion chamber forms a tumble flow Ft. Since the crown surface 50 is formed with a plane 55 (first plane) and a recess inter-recess plane 56 (second plane) which are "continuous planes", the tumble flow Ft is obstructed by a depression such as a cavity. Instead, it can flow along the plane 55. Further, since the relationship between the surface areas S1 to S3 is set as described in the above features (1) to (3), the flow of the tumble flow Ft is weakened by the presence of the exhaust side inclined surface 53 and the intake side inclined surface 54. It will not change.

Due to the structural ingenuity of the crown surface 50, the resistance of the crown surface 50 to the tumble flow Ft is reduced, and the tumble flow Ft can easily continue its flow in the combustion chamber 6. That is, it is possible to reduce the rate at which the tumble flow Ft collides with the exhaust side inclined surface 53, the inner wall of the cylinder 2, and the like and disappears, so that the tumble flow Ft can be easily maintained until the latter half of the compression stroke. When the tumble flow Ft collapses, turbulent energy is generated. Maintaining the tumble flow Ft leads to maintaining the turbulent energy inherent in the tumble flow Ft in a high state without loss due to the collision. Therefore, the tumble flow Ft is disintegrated in the latter half of the compression stroke to generate high turbulent energy, so that the combustion speed of the air-fuel mixture in the combustion chamber 6 can be increased.

In the combustion chamber 6, flame propagation combustion of the air-fuel mixture occurs starting from the ignition operation of the spark plug 16. Here, when the cylinder 2 is set to a high compression ratio, the pressure and temperature in the combustion chamber 6 excessively rise at the compression end of the piston 5 to induce abnormal combustion. The abnormal combustion is a steep self-ignition of unburned fuel gas before the completion of flame propagation combustion, and causes knocking. However, by maintaining the tumble flow Ft until the latter half of the compression stroke and increasing the combustion speed, it is possible to complete the combustion before the self-ignition that causes knocking occurs. Since knocking can be suppressed, it is possible to avoid control that intentionally suppresses the engine output, for example, control such as controlling the fuel injection timing of the injector 15 to retard the combustion center of gravity. Further, as a result, a high compression ratio of the cylinder 2 can be achieved, and fuel efficiency can be improved.

Subsequently, a comparative example that does not satisfy the above features (1) to (3) will be described. FIG. 9B is a diagram schematically showing the flow of the tumble flow Ft in the combustion chamber 6 when the crown surface 50 that does not satisfy the above feature (1) is adopted. The tumble flow Ft is a flow that enters the combustion chamber 6 from the IN side, turns at the inner wall of the cylinder 2 on the EX side, and goes toward the IN side along the crown surface 50. When the above feature (1) is not satisfied, that is, when the surface area S2 of the exhaust side inclined surface 53 is larger than the total surface area S1 of the plane 55 and the plane between recesses 56, the tumble flow Ft collides with the exhaust side inclined surface 53. It becomes easier and the ratio of the tumble flow Ft maintained until the latter half of the compression stroke decreases. That is, as shown in FIG. 9B, a part of the tumble flow Ft1 goes from the EX side to the IN side so as to be guided by the plane 55, while the other part of the tumble flow Ft2 is in the turn. This is because it later collides with the exhaust side inclined surface 53 and collapses. As described in the feature (1), by setting the surface area S1 to be larger than the surface area S2 of the exhaust side inclined surface 53, it is possible to reduce the tumble flow Ft that collides with the exhaust side inclined surface 53 and disappears.

FIG. 10A is a diagram schematically showing the flow of the tumble flow Ft in the combustion chamber 6 when the above feature (2) is not satisfied. When the above feature (2) is not satisfied, that is, when the surface area S3 of the intake side inclined surface 54 is larger than the surface area S1, the flow of the derived flow Ft3 along the intake side inclined surface 54 is likely to be formed. The derived flow Ft3 is a flow that deviates from the path of the tumble flow Ft, which is the main flow, and is guided by the intake side inclined surface 54 and becomes a flow toward the IN side inner wall surface of the cylinder 2. Eventually, the derived flow Ft3 collides with the inner wall surface of the cylinder 2 and disappears. Therefore, the derived flow Ft3 becomes a loss of the tumble flow Ft, and reduces the tumble flow Ft maintained until the latter half of the compression stroke. As shown in the feature (2), by setting the surface area S1 of the plane 55 and the plane between recesses 56 to be larger than the surface area S3 of the intake side inclined surface 54, the derived flow toward the inner wall of the cylinder 2 along the intake side inclined surface 54. Ft3 can be suppressed.

By satisfying at least the above-mentioned feature (1), the maintainability of the tumble flow Ft can be enhanced. In addition to this, by satisfying the feature (2), the maintainability of the tumble flow Ft can be further improved. Further, after satisfying the features (1) and (2), as in the feature (3), the total surface area S1 of the plane 55 and the plane between recesses 56 is combined with the surface area S2 of the exhaust side inclined surface 53 and the intake side inclined surface 54. It is desirable to set it larger than the total surface area of S3. As a result, the collision of the tumble flow Ft with the exhaust side inclined surface 53 shown in FIG. 9 (B) and the cylinder 2 due to the tumble flow Ft being guided by the intake side inclined surface 54 shown in FIG. 10 (A). The collision with the inner wall on the IN side can be further suppressed, and the maintainability of the tumble flow Ft can be further improved.

FIG. 10B is a diagram schematically showing the flow of the tumble flow Ft in the combustion chamber 6 when the plane 55 is not a “continuous plane”. A typical example in which the plane 55 is not a “continuous plane” is a case where the cavity 59 is formed in the plane 55, and FIG. 10 (B) shows the embodiment. The cavity 59 is a portion in which the center region of the plane 55 is recessed in a bowl shape. In this case, the surface area S1 becomes small, and it becomes difficult to satisfy the above features (1) to (3). Further, the flow of the tumble flow Ft is obstructed by the cavity 59. That is, a part of the tumble flow Ft becomes a derivative flow Ft4 that enters the recess of the cavity 59. The derived flow Ft4 collides with the wall surface of the cavity 59 and disappears. Therefore, the derived flow Ft4 becomes a loss and reduces the tumble flow Ft maintained until the latter half of the compression stroke. Therefore, it is significant that the plane 55 is a "continuous plane".

[About other features of the combustion chamber structure]
Subsequently, the features of the combustion chamber structure other than the above surface areas S1 to S3 will be described. First, regarding Lie / h, which is the ratio of the width Lie, which is the width in the Y direction of the plane 55, to the mountain height h, in the range of compression ratio = 13.5 to 15.5.
2.5 <Lie / h <9.0 ... (A)
It is desirable to satisfy the relationship of.

In the combustion chamber 6 provided with the pent-roof type combustion chamber ceiling surface 6U, the inclination angles of the exhaust side inclined surface 53 and the intake side inclined surface 54 of the crown surface 50 are substantially along the inclination angle of the combustion chamber ceiling surface 6U. .. Therefore, the mountain height h greatly affects the width Lie of the plane 55. Increasing the mountain height h leads to increasing the compression ratio. For example, if the mountain height h is set high in an attempt to improve fuel efficiency, the width Lie becomes narrow. That is, the surface area of the plane 55 becomes smaller. In this case, even if the fuel efficiency is improved, it becomes difficult to maintain the tumble flow Ft until the latter half of the compression stroke. After all, in order to prevent knocking, suppression control of engine output is required. However, by setting Lie / h within the range of the above formula (A), it is possible to achieve both improvement in fuel efficiency and improvement in engine output. From the viewpoint of making this compatibility more desirable, Lie / h is used in the range of compression ratio = 13.5 to 15.5.
5.0 <Lie / h <9.0 ... (A1)
It is desirable to satisfy the relationship of.

Next, regarding Lfr / h, which is the ratio between the front-rear width Lfr, which is the width in the X direction of the plane 55, and the mountain height h, in the range of compression ratio = 13.5 to 15.5,
12.0 <Lfr / h <16.0 ... (B)
It is desirable to satisfy the relationship of.

Similar to the horizontal width Lie, the higher the mountain height h is set, the narrower the front-rear width Lfr becomes and the smaller the surface area of the plane 55. Therefore, it becomes difficult to maintain the tumble flow Ft until the latter half of the compression stroke, and it is necessary to suppress the engine output. However, by setting Lfr / h within the range of the above equation (B), it is possible to achieve both improvement in fuel efficiency and improvement in engine output. From the viewpoint of making this compatibility more desirable, Lfr / h is set in the range of compression ratio = 13.5 to 15.5.
13.5 <Lfr / h <14.5 ... (B1)
It is desirable to satisfy the relationship of.

Here, it is desirable that the front-rear width Lfr of the plane 55 is larger than the width Lie. As schematically shown in FIG. 2, the tumble flow Ft is introduced into the combustion chamber 6 from the intake port 9, folds back at the inner wall surface on the EX side of the cylinder 2, passes over the flat surface 55, and heads toward the IN side. If the front-rear width Lfr is smaller than the width Lie and the plane 55, there is no plane at the ends of the crown surface 50 on the + X side and the −X side. In this case, it becomes difficult for the tumble flow Ft to be guided at the ends on the + X side and the −X side, and a flow loss occurs. On the other hand, by setting the plane 55 having a front-rear width Lfr larger than the width Lie, the tumble flow Ft can be guided even at the ends on the + X side and the −X side, and the maintainability of the tumble flow Ft can be improved. ..

The compression ratio = 13. In the range of 5 to 15.5
5000 <(Exd × S1) / h <18000 ... (C)
It is desirable to satisfy the relationship of.

Since the tumble flow Ft flows as described above, the smaller the exhaust side inclined surface angle Exd, the more the flow of the tumble flow Ft is changed at the boundary between the exhaust side inclined surface 53 and the plane 55, or the exhaust side. It is possible to suppress the degree of collision with the inclined surface 53. However, the compression ratio cannot be increased unless the mountain height h is set to a certain height. In order to increase the mountain height h and increase the surface area of the plane, it is necessary to increase the exhaust side inclined surface angle Exd. In consideration of these contradictory requirements, in order to achieve both high compression ratio and maintenance of tumble flow Ft, (Exd × S1) / h may be set in the range of the above equation (C). From the viewpoint of making this compatibility more desirable, (Exd × S1) / h is set in the range of compression ratio = 13.5 to 15.5.
7000 <(Exd × S1) / h <12000 ... (C1)
It is desirable to satisfy the relationship of.

Next, in the combustion chamber 6 partitioned by the crown surface 50 having the flat surface 55, a shape device capable of forming the same in-cylinder flow in the combustion chamber 6 even if the displacement of the engine body 1 is different is shown. As shown in FIG. 3, by regulating the flow of intake air in the second intake port 9B with the swirl valve 17, a swirl flow Fs which is a lateral vortex is formed as an in-cylinder flow in the combustion chamber 6. In the present embodiment, the swirl flow Fs is a diagonal swirl flow mixed with the tumble flow Ft.

When the displacement of the engine body 1 is different, the bore diameter Lb and the stroke Ls (FIG. 2) are also different. The bore diameter Lb is the inner diameter of the cylinder 2 and is a length substantially corresponding to the diameter of the piston 5. The stroke Ls is the length at which the piston 5 moves in the Z direction between TDC (top dead center) and BDC (bottom dead center). The flow of swirl flow Fs changes when the engine displacement is different, even if the engine speed and load are the same. Therefore, for example, in a combustion simulation or the like, calibration according to the flow of swirl flow Fs is required for each displacement, which is a bottleneck in engine development.

The flow of the swirl flow Fs is greatly affected by the relationship between the mountain height h and the stroke Ls of the piston 5. Even if the engine displacement is different, the ratio of the mountain height h and the stroke Ls is from the viewpoint of making the flow of the swirl flow Fs the same and realizing the same combustion in the combustion chamber 6 at the same engine speed and the same load. For h / Ls, in the range of compression ratio = 13.5 to 15.5,
0.045 <h / Ls <0.065 ... (D)
It is desirable to satisfy the relationship of.

When the mountain height h is high and the stroke Ls is small, the swirl flow Fs easily collides with the raised portion (exhaust side inclined surface 53, intake side inclined surface 54 and flat surface 55) of the crown surface 50 of the piston 5, and the swirl flow Fs is generated. Decay. On the other hand, when the mountain height h is low and the stroke Ls is large, the distance that the swirl flow Fs contacts the inner wall surface of the cylinder 2 becomes long, which also causes the swirl flow Fs to be attenuated. However, by setting h / Ls to the range of the above equation (D), the attenuation of the swirl flow Fs due to the high mountain height h and the attenuation of the swirl flow Fs due to the large stroke Ls can be obtained. Can be equal. Therefore, even when the engine displacement is different, the same swirl flow Fs can be formed in the combustion chamber 6, and the same combustion can be realized in the combustion chamber 6.

Further, the flow of the swirl flow Fs is greatly affected by the relationship between the mountain height h and the bore diameter Lb. Even if the engine displacement is different, the ratio of the mountain height h and the bore diameter Lb is from the viewpoint of achieving the same combustion in the combustion chamber 6 with the same engine rotation speed and the same load by making the flow of swirl flow Fs the same. For a certain h / Lb, in the range of compression ratio = 13.5 to 15.5,
0.055 <h / Lb <0.075 ... (E)
It is desirable to satisfy the relationship of.

When the mountain height h is high and the bore diameter Lb is small, the swirl flow Fs easily collides with the raised portion of the crown surface 50 of the piston 5, and the swirl flow Fs is attenuated. On the other hand, when the mountain height h is low and the bore diameter Lb is large, the distance that the swirl flow Fs comes into contact with the inner wall surface of the cylinder 2 becomes long, which also causes the swirl flow Fs to be attenuated. However, by setting h / Lb to the range of the above equation (E), the attenuation of the swirl flow Fs due to the high mountain height h and the attenuation of the swirl flow Fs due to the large bore diameter Lb can be obtained. Can be made equivalent. Therefore, even when the engine displacement is different, the same swirl flow Fs can be formed in the combustion chamber 6, and the same combustion can be realized in the combustion chamber 6.

[Examples and comparative examples of crown surface design]
11 to 13 are tabular views showing the structure and parameters of the crown surface 50 of the piston 5 according to Examples 1 to 5 and Comparative Examples of the present invention. Here, the piston 5 applied to engines having different displacements is illustrated. The pistons 5 of Examples 1 to 5 and Comparative Examples have a displacement of 1.5 liters, a displacement of Example 6 is 2.0 liters, and a displacement of Example 7 is 2.5 liters.

For each example of FIGS. 11 to 13, an external perspective view and a plan view of the crown surface 50 are shown. Further, the positions and the surface area values of the plane 55, the recess plane 56, the intake side inclined surface 54, and the exhaust side inclined surface 53 are shown, respectively. For the exhaust side inclined surface 53, the surface area of each portion (the surface area of the recess portion 531 and the recess intersection portion 532, and in some cases, the surface area of the recess lower portion 533) is also described. Further, the added value of the surface area of the intake side inclined surface 54 and the surface area of the exhaust side inclined surface 53 is shown as "the total surface area of the inclined surface".

For each example, the turbulent energy ratio (turbulent E ratio) based on the analysis value of the turbulent energy is shown. The analysis value of the turbulent energy is the turbulent energy possessed by the in-cylinder flow (tumble flow Ft) when the piston 5 is at the compression top dead center, and the dedicated software (IDAJ Co., Ltd., software name: CONVERGE) is used. It was derived by the analysis calculation used. The turbulence E ratio is the ratio of the analysis values of the turbulence energy of Examples 1 to 5 when the analysis value of the turbulence energy obtained for the “comparative example” of FIG. 13 is set to “1”. The compression ratio for each example is also shown.

Each of the planes 55 of Examples 1 to 5 is a "continuous plane", and no cavity is formed. On the other hand, the comparative example has a cavity 59 in the radial center region of the crown surface 50. Further, in each of Examples 1 to 5, the recess-to-recess plane 56 is arranged on the exhaust side of the plane 55, but the comparative example does not have a corresponding plane.

In Examples 1 to 5, the total surface area of the plane 55 and the recessed plane 56 is larger than the surface area of the exhaust side inclined surface 53 and the surface area of the intake side inclined surface 54, respectively, and the "total surface area of the inclined surface" is "total surface area". Is a larger example. In Examples 1 to 5, the total surface area of the plane 55 and the recess plane 56 is approximately 2.5 to 5 times the surface area of the exhaust side inclined surface 53, and 2. the surface area of the intake side inclined surface 54. It has a size of about 5 to 4.1 times and a size of about 1.3 to 2.2 times the "total surface area of inclined surfaces". The comparative example is an example in which the surface area of the plane 55 is smaller than the surface area of the exhaust side inclined surface 53 and the surface area of the intake side inclined surface 54.

It can be seen that the turbulent flow E ratio of any of Examples 1 to 5 is larger than the turbulent flow E ratio of the comparative example. Here, the turbulent flow E ratio of Examples 1 to 5 is obtained to be 50% or more larger than the turbulent flow E ratio of the comparative example. From these results, it can be said that in Examples 1 to 5, the maintainability of the tumble flow Ft was enhanced, and most of the tumble flow Ft was successfully destroyed in the latter half of the compression stroke. Therefore, according to Examples 1 to 5, high turbulent energy can be generated in the latter half of the compression stroke, and the combustion speed can be increased.

[Action effect]
According to the combustion chamber structure of the engine according to the present embodiment described above, the following functions and effects are obtained. First, since a continuous plane 55 (first plane) is formed on the crown surface 50, the tumble flow Ft can be flowed along the plane 55 without being obstructed by a depression such as a cavity. Further, since the recess-to-recess plane 56 (second plane) is arranged between the pair of recess portions 531 on the exhaust side inclined surface 53, the tumble flow Ft can be guided by the recess-to-recess plane 56. Therefore, it is possible to prevent the tumble flow Ft from colliding with the boundary portion between the exhaust side inclined surface 53 and the flat surface 55 between the pair of recess portions 531 and weakening.

With reference to FIG. 14, the above advantages will be described. FIG. 14 (A) shows a tumble flow when the crown surface 50 is provided with a recess-to-recess plane 56. Here, the recess interplanet 56 flows through the central region of the crown surface 50 extending in the −Y direction from the plane 55 in the X direction, and the central tumble flow FtC flowing on the −X side and the + X side of the central tumble flow FtC, respectively. The lateral tumble flow FtS is shown.

As shown in FIG. 14A, the central tumble flow FtC flowing from the + YZ direction to the −YZ direction is folded back in the + Y direction on the crown surface 50. At this time, the central tumble flow FtC sequentially flows along the recess-to-recess planes 56 and 55. In the X-direction central region of the crown surface 50 through which the central tumble flow FtC flows, the −Y-side edge of the plane 55 is extended in the −Y direction by the formation of the recess-to-recess plane 56. Therefore, the central tumble flow FtC is less likely to collide with the exhaust side inclined surface 53 or the boundary portion between the exhaust side inclined surface 53 and the plane 55. Therefore, the resistance of the crown surface 50 to the central tumble flow FtC becomes small, and the central tumble flow FtC is less likely to be disturbed or weakened. Therefore, the central tumble flow FtC does not inhibit the lateral tumble flow FtS flowing on both sides, nor does it inhibit the maintainability of the lateral tumble flow FtS.

FIG. 14B is a diagram schematically showing the flow of the central tumble flow FtC when the crown surface 50 is not provided with the recess plane 56. If the recess-to-recess plane 56 does not exist, the central tumble flow FtC tends to collide with the boundary portion 501 between the exhaust side inclined surface 53 and the plane 55. When the collision occurs, a part of the flow FtC1 flows through the original flow path of the central tumble flow FtC, but the flow FtC2 whose path changes to the + X side, the flow FtC3 whose path changes to the −X side, and the like occur. In this case, the central tumble flow FtC itself is weakened, and the flows FtC2 and FtC3 collide with the side tumble flow FtS, and the side tumble flow FtS is also weakened. Therefore, the maintainability of the tumble flow Ft is lowered.

As described above, by forming the plane 55 and the recess plane 56 on the crown surface 50, the maintainability of the tumble flow Ft can be enhanced. Therefore, it is possible to increase the combustion speed by maintaining the tumble flow Ft until the latter half of the compression stroke and then disintegrating it to generate high turbulent energy. As a result, the combustion of the air-fuel mixture in the combustion chamber 6 can be completed before the self-ignition that causes knocking occurs. Since knocking can be suppressed, control that suppresses engine output such as retarding the center of gravity of combustion can be avoided. As a result, a high compression ratio can be achieved.

Further, a spark plug 16 that realizes flame propagation combustion is arranged on the ceiling surface 6U of the combustion chamber facing the flat surface 55 of the crown surface 50. In this embodiment, it is arranged in the center of the combustion chamber 6 (on the cylinder shaft AX). The intake air compressed without weakening the tumble flow Ft is in a state of high turbulent energy at a position facing the plane 55. By arranging the spark plug 16 at such a position, the combustion speed of flame propagation combustion can be increased.

Further, the injector 15 is arranged on the intake side of the combustion chamber 6. This makes it easier to put the fuel sprayed from the injector 15 on the tumble flow Ft, and a homogeneous air-fuel mixture can be formed in the combustion chamber 6.

[Modification example]
Although the embodiments of the present invention have been described above, the present invention can take various modified embodiments. FIG. 15 is a plan view of the crown surface 50A of the piston according to the modified example of the present invention. In this modification, an example is shown in which the crown surface 50A is provided with a plane between recesses 56A (third plane) on the intake side in addition to the plane 55 and the plane 56 between recesses.

On the intake side inclined surface 54A, a pair of intake recess portions 541 that avoid interference with intake valves 11 arranged in the two intake ports 9A and 9B (FIG. 3), and a + Y approach between these intake recess portions 541. An intake recess intersection portion 542 arranged at the position of is formed. The intake-side recess-to-recess plane 56A is a plane that is arranged in the pair of intake recess portions 541 and is continuous in the same plane as the plane 55. The intake-side recess inter-plane plane 56A is a plane that extends from the IN end edge 553, which is the + Y-side end edge of the plane 55, to the + Y side and is connected to the upper end of the intake recess intersection portion 542. According to this modification, the tumble flow Ft can be guided above the combustion chamber 6 along the intake-side recess space plane 56A. That is, it is possible to prevent the tumble flow Ft from flowing along the intake side inclined surface 54A and colliding with the intake side inner wall surface of the cylinder 2 to be weakened.

1 Engine body 11 Intake valve 12 Exhaust valve 15 Injector (fuel injection part)
16 Spark plug (ignition part)
2 Cylinder 5 Piston 50 Crown surface 51 Exhaust side bottom 52 Intake side bottom 53 Exhaust side inclined surface 54 Intake side inclined surface 55 Plane (first plane)
56 Recess plane (second plane)
56A Intake side recess plane 56A (third plane)
6 Combustion chamber 6U Combustion chamber ceiling surface (pent roof type ceiling surface)
9 Intake port 10 Exhaust port AX Cylinder shaft Fs swirl flow Ft tumble flow

Claims (6)

A combustion chamber structure of an engine including a combustion chamber partitioned by a crown surface of a piston, an inner wall surface of a cylinder in which the piston is slidably housed, and a pent-roof type ceiling surface formed on a cylinder head. hand,
On the ceiling surface, an opening of two intake ports for supplying intake air to the combustion chamber and an opening of two exhaust ports for discharging exhaust gas from the combustion chamber are formed, and the side on which the intake port is arranged. Is the intake side, and the side on which the exhaust port is arranged is the exhaust side.
The crown surface is
An exhaust side bottom portion arranged near the exhaust side edge of the crown surface, and an intake side bottom portion arranged near the intake side edge.
An inclined surface that rises from the bottom of the exhaust side toward the center of the crown surface, and has an exhaust side inclination provided with a pair of recess portions that avoid interference with the exhaust valves arranged in the two exhaust ports. Face and
An intake-side inclined surface that rises from the intake-side bottom to the center of the crown surface,
A first plane that is continuously provided between the upper end of the exhaust side inclined surface and the upper end of the intake side inclined surface and extends in a direction orthogonal to the axial direction of the cylinder at the central portion of the crown surface.
A combustion chamber structure of an engine, which is arranged between the pair of recess portions of the exhaust side inclined surface and includes a second plane which is continuous in the same plane as the first plane. In the combustion chamber structure of the engine according to claim 1,
When the direction from the intake side to the exhaust side is the first direction, the second plane is formed so as to extend in the first direction from the side side of the first plane on the exhaust side.
The extension length of the second plane is set to a length of at least 1/4 or more of the width of the recess portion in the first direction in the top view of the crown surface, the combustion chamber structure of the engine. In the combustion chamber structure of the engine according to claim 1 or 2.
An engine combustion chamber structure in which an ignition unit that realizes flame propagation combustion is arranged in the combustion chamber on the ceiling surface facing the first plane. In the combustion chamber structure of the engine according to any one of claims 1 to 3.
A combustion chamber structure of an engine in which a fuel injection unit that injects fuel into the combustion chamber is arranged on the intake side of the combustion chamber. In the combustion chamber structure of the engine according to any one of claims 1 to 4.
The intake side inclined surface includes a pair of intake recess portions that avoid interference with intake valves arranged in the two intake ports, respectively.
A combustion chamber structure of an engine which is arranged between the pair of intake recess portions of the intake side inclined surface and further includes a third plane which is continuous in the same plane as the first plane. In the combustion chamber structure of the engine according to any one of claims 1 to 5.
The combustion chamber structure of an engine in which the geometric compression ratio of the cylinder is set within the range of 13.5 or more and 15.5 or less.

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